Funding is requested for a four-year period to conduct a longitudinal prospective study of the role of drug use and other factors in the course of homelessness among men and women who are homeless without kin (single adults). Four-hundred subjects experiencing their first episode of literal homelessness will be recruited from municipal shelter assessment centers in New York City, the central portals of entry into the shelter care system in the region. The sample will be stratified by psychiatric severity and gender. Study subjects will be interviewed at baseline, contacted monthly, and interviewed in depth at six, twelve, and eighteen months, employing a protocol that covers the factors predicted to influence the course of homelessness. An assertive follow-up strategy will be employed to better guarantee minimal attrition over the course of the study. Study hypotheses posit that drug use and drug use disorders that are current during the 18-month follow-up period will prolong the return to conventional housing independently, and also by increasing the risk for psychiatric co-morbidity, inadequate family support, unemployment, failure to obtain entitlement income, and failure to obtain access to housing programs. The relationship of drug use and drug use disorders to use of mental health and substance abuse treatment services and antecedent characteristics will also be investigated. Structured behavioral assessments to be employed in the study include a research diagnostic instrument designed specifically for comorbid substance and mental disorders. Study of the role of drug use as a risk factor for chronic homelessness will shed new light on the adverse behavioral and social consequences of drug use. Greater understanding of factors that determine the course of homelessness has implications for the development of prevention and early intervention strategies.